This invention relates to electrical penetrators, sometimes referred to as feedthrough devices.
Electrical penetrators are used to transmit electricity, usually at high voltage and high amperage (e.g., 5,000 volts at 150 amperes) through barrier walls of bulkheads, pressure vessel housings, wellheads, downhole packers, etc. Frequently, the penetrators are subjected to high and variable pressure differentials that exist across the barrier walls, in addition to high and variable temperatures. A penetrator must be able to maintain a pressure seal and electrical integrity in hostile environments while operating to conduct electricity, and also while not operating.
A typical existing penetrator design for downhole use comprises three major parts--a power feedthrough mandrel in the middle of the device, a surface plug connector at the top of the mandrel (that is spliced to the surface power cable), and a lower plug connector at the bottom of the mandrel (that is spliced to the downhole power cable). The mandrel comprises electrical conductors insulated with rubber and molded in place within a shell by epoxy, for example. The plug connectors at the top and bottom of the mandrel are encapsulated with rubber. Sealing is achieved through compression of the rubber parts.
In general, existing penetrator designs rely upon maintenance of contact force between an elastomeric sealing block, a conductor, conductor insulation, and an adjacent metal shell, initial sealing block contact force being established by mechanically compressing the sealing block. Maintenance of the contact force, and hence the seal integrity, during the life of the penetrator depends on the elastic properties of the elastomer of the sealing block. During periods of high operating temperature, the elastomeric sealing block expands, and the elastomeric material may take a compression set (a well-known property of elastomers). When this occurs, and the operating temperature returns to normal or lower temperature, the contact force will be insufficient to maintain the seal integrity. Consequently, leakage paths develop between adjacent internal parts, and the penetrator fails. An additional problem occurs when the sealing block is trapped within the shell of the penetrator with no expansion volume allowance and is exposed to hydrocarbons that cause swelling of the elastomer. Expansion of the elastomer in the absence of an expansion volume allowance causes mechanical or structural damage, such as extrusion of insulation off of current-carrying conductors of the penetrator and cracking of insulating materials in the penetrator shell.